Prior art processes for ABS polyblends have generally grafted diene rubber particles contained in aqueous emulsion with alkenyl aromatic and alkenyl nitrile monomers to form grafted rubber phase particles dispersed in a matrix phase of said monomers.
The rubber particle size in such rubber emulsions ranges generally from about 0.01 to 0.50 microns which will toughen the matrix phase if incorporated in relatively high concentrations, i.e., 10 to 25% by weight.
The surface gloss of such polyblends is high, as extruded into profiles or molded into articles, because the particle size is too small to disturb the surfaces of the article.
U.S. Pat. No. 3,509,237 discloses that the toughness of ABS polyblends can be improved by adding large particles of grafted rubber, i.e., in the range of about 1 to 2.5 microns to ABS polyblends having rubber particles ranging from 0.01 to 0.50 microns.
It was noted that the large particles lowered gloss and no more than about 3 to 30% of large particles could be used to improve toughness and yet maintain reasonable gloss. Gloss as measured by the well known Hunter Gloss Test could be reduced from about 90 to about 60 using up to about 50% large particles.
Recent commercial requirements for extruded sheet and molding require higher gloss and toughness without the use of large particles of about 0.7 to 3 microns to toughen the polyblend. It has now been discovered that if the smaller rubber particles can be grafted more efficiently with larger amounts of monomers as a superstrate that the particles will toughen the polyblend substantially yet provide high gloss to extruded and molded polyblend parts.
In particular, alkenyl aromatic and alkenyl nitrile monomers can be grafted in larger amounts and with greater efficiency to rubber particles in latices by emulsion polymerization if the monomers have present about 1 to 30% by weight of a myrcene present during polymerization. The mechanism is not completely understood but it is believed that the myrcene has a conjugated diene structure present which is highly reactive with the unsaturated rubber substrate and provides multiple sites for the alkenyl monomers to graft to increasing the efficiency and amount of grafting superstrate monomers which can be placed on the rubber particle substrate. Such higher levels of superstrate are believed to increase the compatibility of the rubber particles in the matrix phase giving substantially improved gloss and toughness.